Dams in the upper Mekong River modify nutrient bioavailability downstream

March 17, 2020

The number of hydropower dams has increased dramatically in the last 100 years for energy supply, climate change mitigation, and economic development. However, recent studies have overwhelmingly stressed the negative consequences of dam construction. Notably, it is commonly assumed that reservoirs retain nutrients, and this nutrient reduction significantly reduces primary productivity, fishery catches and food security downstream. Such perception largely hampers electricity supply and even sustainable socio-economic development in many developing regions such as Congo and lower Mekong basins.

However, solid scientific support for the widespread belief that dams retain nutrients is usually lacking, because monitoring programs gathering data to establish how nutrient fluxes and phytoplankton production have changed after dam construction are rare. A new article by Qiuwen Chen and his research group at Nanjing Hydraulic Research Institute, China, together with Prof. Jef Huisman from the University of Amsterdam and Prof. Stephen C Maberly from UK Centre for Ecology & Hydrology now provides extensive monitoring data for the upper Mekong River. Their data reveal some surprising new insights.

Contrary to expectation, their study shows that a cascade of reservoirs along the upper Mekong River increased downstream bioavailability of nitrogen and phosphorus. The core mechanism is the synergic effect of increased hydraulic residence time and the development of hypoxic conditions due to stratification and organic matter accumulation. The lack of oxygen results in release of nutrients from the sediment and subsequent accumulation of ammonium and phosphorus in the deeper water layers of the reservoir, which enhances the concentration of dissolved nutrients released downstream from the base of the reservoirs.

Moreover, the longer residence time in the reservoirs strongly increased phytoplankton production, with a shift in species composition from diatoms upstream to green algae in the downstream reservoirs.

Upstream dams are regularly blamed for nutrient retention and consequently the collapse of primary productivity and fisheries, and even human rights of subsistence in the lower Mekong River. This work implies that the fishery decline in the lower Mekong River might be caused by other factors such as over-fishing, habitat modification, disruption of fish migration by dam construction or water quality deterioration from local sources, rather than a reduction in nutrient availability or primary productivity induced by the cascade dams upstream.

This novel perspective on the globally important issue emphasizes the need for dedicated monitoring of the environmental impacts of hydropower dams on nutrient cycling and primary production. The findings are of great significance not only for science, but also for sustainable social-economic development along the Mekong River and other transboundary rivers worldwide.
-end-
See the article: Chen Q, Shi W, Huisman J, Maberly SC, Zhang J, Yu J, Chen Y, Tonina D, Yi Q, 2020. Hydropower reservoirs on the upper Mekong River modify nutrient bioavailability downstream. National Science Review, doi: 10.1093/nsr/nwaa026

Link: https://doi.org/10.1093/nsr/nwaa026

Science China Press

Related Phosphorus Articles from Brightsurf:

Blue phosphorus: How a semiconductor becomes a metal
Blue phosphorus, an atomically thin synthetic semiconductor, becomes metallic as soon as it is converted into a double layer.

Phosphorus deficit may disrupt regional food supply chains
Phosphorus-based fertilizer is essential in modern agriculture. In regions with high population growth, more phosphorus will be needed to produce more food.

SwRI scientist searches for stellar phosphorus to find potentially habitable exoplanets
SAN ANTONIO -- Sept. 16, 2020 -- A Southwest Research Institute scientist has identified stellar phosphorus as a probable marker in narrowing the search for life in the cosmos.

Worldwide loss of phosphorus due to soil erosion quantified for the first time
Phosphorus is essential for agriculture, yet this important plant nutrient is increasingly being lost from soils around the world.

Stars rich in phosphorus: Seeds of life in the universe
The journal Nature Communications today is publishing the discovery of a new type of stars, very rich in phosphorus, which could help to explain the origin of this chemical element in our Galaxy.

Black phosphorus future in 3D analysis, molecular fingerprinting
Many compact systems using mid-infrared technology continue to face compatibility issues when integrating with conventional electronics.

Fostering a sustainable use of phosphorus
Phosphorus is critical to food security, ecosystem functioning and human activities.

Newly discovered plant gene could boost phosphorus intake
Researchers from the University of Copenhagen have discovered an important gene in plants that could help agricultural crops collaborate better with underground fungi -- providing them with wider root networks and helping them to absorb phosphorus.

Anaerobically disinfect soil to increase phosphorus using diluted ethanol
Anaerobic disinfection of soil is an effective method to kill unwanted bacteria, parasites and weeds without using chemical pesticides.

Graphene heterostructures with black phosphorus, arsenic enable new infrared detectors
MIPT scientists and their colleagues from Japan and the U.S.

Read More: Phosphorus News and Phosphorus Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.